Comparing the nine‐item Shared Decision‐Making Questionnaire to the OPTION Scale – an attempt to establish convergent validity

Abstract Background While there has been a clear move towards shared decision‐making ( SDM ) in the last few years, the measurement of SDM ‐related constructs remains challenging. There has been a call for further psychometric testing of known scales, especially regarding validity aspects. Objective To test convergent validity of the nine‐item S hared D ecision‐ M aking Q uestionnaire ( SDM ‐ Q ‐9) by comparing it to the OPTION S cale. Design Cross‐sectional study. Setting and participants Data were collected in outpatient care practices. Patients suffering from chronic diseases and facing a medical decision were included in the study. Methods Consultations were evaluated using the OPTION Scale. Patients completed the SDM ‐ Q ‐9 after the consultation. First, the internal consistency of both scales and the inter‐rater reliability of the OPTION Scale were calculated. To analyse the convergent validity of the SDM ‐ Q ‐9, correlation between the patient ( SDM ‐ Q ‐9) and expert ratings ( OPTION S cale) was calculated. Results A total of 21 physicians provided analysable data of consultations with 63 patients. Analyses revealed good internal consistency of the SDM ‐ Q ‐9 and limited internal consistency of the OPTION S cale. Inter‐rater reliability of the latter was less than optimal. Association between the total scores of both instruments was weak with a S pearman correlation of r = 0.19 and did not reach statistical significance. Discussion By the use of the OPTION S cale convergent validity of the SDM ‐ Q ‐9 could not be established. Several possible explanations for this result are discussed. Conclusion This study shows that the measurement of SDM remains challenging.